Even better than mulching with just leaves is mulching with both leaves and grass clippings. This will help the leaves to break down faster and keep them form pulling nitrogen from your soil.
As the posters before me have said: start your compost pile. We have an excellent forum here for learning about and discussing making compost. This is going to be one of the most important factor in improving the quality of your soil.
Also, you can try planting a cover-crop. This involves planting a certain crop in the fall, then tilling it in come spring. Crops that are good fro this include rye, alfalfa, soybeans, hairy vetch, crimson clover, and more. Some you till in the spring, others can be tilled before winter.
Good luck with your new garden